A Solution‐Processable Dithienyldiketopyrrolopyrrole Dye Molecule with Acetylene as a π‐Linkage for Organic Solar Cells

We present the efficient synthesis and photovoltaic response of a linearly conjugated molecule DT‐DPP (AAnAT) 2 , which contains a dithienyldiketopyrrolopyrrole core symmetrically connected through a 9,10‐anthracenyl unit to 3‐alkylthiophene via an acetylene linkage. The compound is crystalline with a T m of 204 °C. The as‐cast film has a main broad absorption at 650 nm with a shoulder at 737 nm, tailing until ca. 800 nm. The HOMO level was estimated as −5.26 eV, derived from the first reversible electron oxidation wave at ca. 0.93 V vs. Ag/AgCl reference electrode. The space charge limited current hole mobility of a pristine film is ca. 2.90×10 −4  cm 2  V −1  s −1 . The preliminary characterization of simple bulk heterojunction solar cells provides a power conversion efficiency (PCE) of ca. 4.0 % with V OC =0.77 V, J SC =10.0 mA cm −2 , and FF =52 %, based on the as‐cast active layer without a processing additive or solvent vapor annealing. Thermal annealing the active layer at a mild temperature of 50 °C increased the PCE to 4.39 % due mainly to the improvement of the FF .